On 07/10/2011 09:44 AM, Oleg Nesterov wrote:> handle_signal()->set_fs() has a nice comment which explains what> set_fs() is, but it doesn't explain why it is needed and why it> depends on CONFIG_X86_64.> > Afaics, the history of this confusion is:> > 1. I guess today nobody can explain why it was needed> in arch/i386/kernel/signal.c, perhaps it was always> wrong. This predates 2.4.0 kernel.> > 2. then it was copy-and-past'ed to the new x86_64 arch.> > 3. then it was removed from i386 (but not from x86_64)> by b93b6ca3 "i386: remove unnecessary code".> > 4. then it was reintroduced under CONFIG_X86_64 when x86> unified i386 and x86_64, because the patch above didn't> touch x86_64.> > Remove it. ->addr_limit should be correct. Even if it was possible> that it is wrong, it is too late to fix it after setup_rt_frame().>

The main reason I could think of why this would be necessary is if wetake an event while we have fs == KERNEL_DS inside the kernel which isthen promoted to a signal. Are you absolutely sure that can't happen?

In particular, there should be a setting upstream of this, as you'recorrectly pointing out that it's too late. If not, we might actuallyhave a problem.